Prior Art
A good deal of prior art exists in the field of remote control devices and keyboards in which the control information is linked via either an audio or optical path so as to avoid the use of cables, wires and the like. Typical examples are the well known remote control channel selection utilized in many home TV sets. These devices utilized either sonic or ultrasonic codes or, in the alternative, often use infra red transmitters with a receiver at the base station or TV set. The general usage of infra red links for data processing input from keyboards or terminals to a large using system has also been investigated as shown by the IEEE article "Infra Red Communication for In House Applications," by F. R. Gfeller et al, appearing at pages 132-138 reprint number CH1388-8/78/000, copyright 1978, IEEE.
In all of these applications for remotely linked data input or control devices utilized without cables or physical connection, a possibility exists that the remote control device or keyboard will be self-powered, i.e., by a battery or the like. Typical dry cell batteries exhibit a declining voltage versus power-on time characteristic over their life. Eventually, the total battery voltage available will decrease to the point that unstable communication or control exists. At this point, the keyboard or control mechanism will fail and will cause the user to experience inconvenience, especially if no spare batteries are available. A low voltage battery warning indicator is clearly called for. However, a variety of these low battery voltage indicators that are available such as audible or visual indicators and enunciators consume much more power than the infra red transmitter itself. Once the overall battery voltage has dropped to be within the danger zone, the use of such an indicator could greatly worsen the battery's condition at the most critical time.
An additional factor is that dry cell batteries typically exhibit a declining voltage with time regardless of use, but it is only desirable to actually indicate low voltage condition when an operator is present and the device is in use so that corrective action may be taken.